We extend SAGBI basis theory to quotient rings and explain how the quotient
ring SAGBI algorithm can be used to compute invariants. By an investigatio
n of monomial subalgebras in quotients by binomial ideals, the algorithm is
shown to terminate for computing invariants of the action of a torus or a
finite abelian group. (C) 1999 Published by Elsevier Science B.V. All right
s reserved.